In a variety of orthopaedic procedures, a surgeon must use a clamp to hold a bone in a stationary position. Often, the clamping is required so that the surgeon may steady the bone so that he may perform some cutting or other procedure on the bone, or the surgeon may clamp a cemented object to a bone so that the object remains stationary while the cement cures and the object permanently attaches to the bone. One such orthopaedic procedure requiring the use of an orthopaedic clamp is the implantation of a patellar prosthesis.
The patella, commonly known as the kneecap, is a hard bone having an articular surface of cartilage on the posterior side. The articular surface is held in place against the femoral condyles by the patella tendon where it provides leverage that is necessary to a properly functioning knee joint. If the articular surface becomes damaged by trauma or by degeneration, proper knee functioning breaks down, often accompanied by joint pain and immobility. In such situations, a patella prosthesis, sometimes referred to as a button, may be inserted to restore normal functioning to the knee.
Patella prostheses have also been used in total knee replacement surgery to insure a reproducible interaction of a patella with the femoral and tibial portions of the total knee replacement. Usually in such procedures the posterior side of the patella is prepared, sized and reamed so that a patella implant, when fixed to the patella, restores the reconstructed patella to its natural or original thickness.
In one procedure, the patella is prepared for the patellar implant as follows. A patellar holding clamp is placed on the patella with a clamp ring on the posterior side. The patella is then reamed with a patella reamer to a predetermined depth. One method of determining when the reamer has reached the appropriate depth involves placing a guide member on the patellar holding clamp and a stop member on the reamer. The reamer is then urged toward the patella, guided by the guide member and the clamp ring until the stop member abuts the guide member. Clamps useful for this purpose are disclosed, for example, in U.S. Pat. Nos. 5,129,907; 5,284,482; and 5,575,793.
The patellar implant is then inserted, often with a bone cement, into the prepared bed. A patellar holding clamp may be used to push the patellar implant into the prepared bed, or to hold the implant in place while the bone cement cures. Clamps useful for this purpose are shown in U.S. Pat. No. 4,706,660 (clamp 110).
The prior art clamps are generally useful for their intended purposes, but many of the clamps employ a locking feature, often a threaded rod with a threaded knob, that directly squeezes either the jaws of the clamp or the handle members of the clamp and increases the compression on the bone held between the jaws. Such locking devices must be carefully employed by a surgeon in order not to over tighten the clamp. In addition, existing clamps are limited to a single type and a single size of jaw member, resulting in the need to maintain an inventory of clamps for each different orthopaedic use or size.